Mn(III) cationic N-alkylpyridylporphyrin mimics of SOD activity have been developed (Spasojevic et al, J. Biol. Chem. 278:6831-6837 (2003), Batinic-Haberle, Methods Enzymol. 349:223-233 (2001), Spasojevic and Batinic-Haberle, Inorg. Chim. Acta. 317:230-242 (2001), Batinic-Haberle et al, J. Biol. Chem. 273:24521-24528 (1998), Batinic-Haberle et al, Inorg. Chem. 38:4011-4022 (1999), Kachadourian et al, Inorg. Chem. 38:391-396 (1999), Batinic-Haberle et al, J. Chem. Soc., Dalton Trans., pgs. 2689-2696 (2002), Ferrer-Sueta et al, J. Biol. Chem. 278:27432-27438 (2003)) the N-ethylpyridyl derivative of which, MnTE-2-PyP5+ (Spasojevic et al, J. Biol. Chem. 278:6831-6837 (2003)), exhibits beneficial antioxidant properties in several animal models of oxidative stress injury (Tao et al. Circulation 108:2805-2811 (2003), Sheng et al, J. Neurotrauma, In press (2003), Sheng et al, Drug News and Perspectives 15:654-665 (2002), Sheng et al, Free Radic. Biol. Med. 33:947-961 (2002), Vujaskovic et al, Free Radic. Biol. Med. 33:857-863 (2002), Piganelli et al, Diabetes 51:347-355 (2002), Trostchansky et al, Free Radic. Biol. Med. 35:1293-1300 (2003), Mackensen et al, J. Neurosci. 21:4582-4592 (2001), Aslan et al, Proc. Natl. Acad. Sci. USA 98:15215-15220 (2001), Sheng et al, Free Radic. Biol. Med. In preparation (2003)). Based on the structure-activity relationship, that revealed the key roles of metal-centered redox potential (Batinic-Haberle et al, Inorg. Chem. 38:4011-4022 (1999)) and electrostatics (Spasojevic et al, J. Biol. Chem. 278:6831-6837 (2003)) on the superoxide (O2.−) dismuting ability, a similar compound, N,N′-diethylimidazolyl derivative, MnTDE-2-ImP5+, was synthesized and was proven effective in vivo (Sheng et al, Drug News and Perspectives 15:654-665 (2002), Sheng et al, Free Radic. Biol. Med. 33:947-961 (2002), Sheng et al, Free Radic. Biol. Med. In preparation (2003), Bottino et al, Diabetes 51:2561-2567 (2002), Bowler et al, Free Radic. Biol. Med. 33:1141-1152 (2002)). Besides dismuting O2.−, Mn(III) ortho N-alkylpyridylporphyrins are able to efficiently scavenge peroxynitrite (k>107M−1 s−1) (Ferrer-Sueta et al, J. Biol. Chem. 278:27432-27438 (2003), Ferrer-Sueta et al, Chem. Res. Toxicol. 12:442-449 (1999)) and carbonate radical (k>108 M−1 s−1) (Ferrer-Sueta et al, J. Biol. Chem. 278:27432-27438 (2003)). In addition, these Mn porphyrins undergo reductive nitrosylation with NO. (Spasojevic et al, Nitric Oxide: Biology and Chemistry 4:526-533 (2000)). Finally, they are readily reduced by cellular reductants such as ascorbic acid (Batinic-Haberle et al, J. Chem. Soc., Dalton Trans., pgs. 2689-2696 (2002), Ferrer-Sueta et al, Chem. Res. Toxicol. 12:442-449 (1999), Spasojevic et al, Nitric Oxide: Biology and Chemistry 4:526-533 (2000), Bloodsworth et al, Free Radic. Biol. Med. 28:1017-1029 (2000)), glutathione (Spasojevic et al, Nitric Oxide: Biology and Chemistry 4:526-533 (2000)), tetrahydrobiopterin (Spasojevic and Fridovich, Free Radic. Biol. Med. 33(Suppl. 2):S316 (2002)), and uric acid (Trostchansky et al, Free Radic. Biol. Med. 35:1293-1300 (2003), Ferrer-Sueta et al, Chem. Res. Toxicol. 12:442-449 (1999)). Thus, the catalytic elimination of O2.−, ONOO−, and CO3.− by Mn porphyrins is likely made possible in vivo through coupling with cellular reductants. Through modulation of the levels of reactive oxygen (ROS) and nitrogen (RNS) species, Mn porphyrins can favorably affect cellular redox status and redox sensitive signaling processes (Mikkelsen and Wardman, Oncogene 22:5734-5754 (2003), Chen et al, Free Radic. Biol. Med. 35:117-132 (2003)).
In vivo studies (Trostchansky et al, Free Radic. Biol. Med. 35:1293-1300 (2003), Sheng et al, Free Radic. Biol. Med. In preparation (2003)) indicated that the efficacy of Mn porphyrins can be improved by increasing their lipophilicity. Hence, a series of ortho N-alkylpyridylporphyrins were prepared, wherein the length of N-pyridyl alkyls was increased from methyl to n-octyl (Batinic-Haberle et al, S. Chem. Soc., Dalton Trans., pgs. 2689-2696 (2002)). While all Mn porphyrins of the series can scavenge O2.− (Batinic-Haberle et al, J. Chem. Soc., Dalton Trans., pgs. 2689-2696 (2002)) and ONOO− (Ferrer-Sueta et al, J. Biol. Chem. 278:27432-27438 (2003)) with nearly equal effectiveness, their in vivo performance differs greatly. An increase in the length of the alkyl chains increases lipophilicity up to 10-fold (Batinic-Haberle et al, J. Chem. Soc., Dalton Trans., pgs. 2689-2696 (2002)). Consequently, their bioavailibility can be expected to increase as well. However, as the alkyl chains lengthen, the surfactant character of the porphyrin increases, leading to the potential for increased toxicity. At higher concentrations this effect may predominate over any gain in activity resulting from increased bioavailibility. An attempt was made to overcome the toxicity by working at low concentrations where the sole impact of lipophilicity would be assessed.
The present invention results from studies involving modification of the ortho N-alkylpyridyl and di-ortho N,N′-dialkylimidazolyl chains by introducing ether oxygen. 2-Methoxyethyl analogues of MnTE-2-PyP5+ (FIG. 1, MnTMOE-2-PyP5+) and of MnTDE-2-ImP5+ (FIG. 1, MnTDMOE-2-ImP5+) were synthesized. When compared to ortho pyridylporphyrins, di-ortho imidazolyl compounds have both imidazolyl nitrogens substituted with ethyl(methyl) or methoxyethyl groups. The ortho N-alkylpyridylporphyrins exist as a mixture of positional (atropo-)isomers (Spasojevic et al, Inorg. Chem. 41:5874-5881 (2002)), whereas di-ortho imidazolyl compounds with eight identical imidazolyl substituents do not have positional isomers. As described in the Example that follows, the potency and toxicity of the new Mn porphyrins were assessed using the SOD-deficient E. coli model of oxidative stress (Batinic-Haberle et al, J. Biol. Chem. 273:24521-24528 (1998), Batinic-Haberle et al, Inorg. Chem. 38:4011-4022 (1999)) which has been proven useful in the past in evaluating prospective candidates for animal models of oxidative stress injuries.